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A007615
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Primes with unique period length (the periods are given in A007498).
(Formerly M2890)
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6
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3, 11, 37, 101, 333667, 9091, 9901, 909091, 1111111111111111111, 11111111111111111111111, 99990001, 999999000001, 909090909090909091, 900900900900990990990991, 9999999900000001
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| Additional terms are Phi(n,10)/gcd(n,Phi(n,10)) for the n in A007498, where Phi(n,10) is the n-th cyclotomic polynomial evaluated at 10.
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REFERENCES
| N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
Samuel Yates, Period Lengths of Exactly One or Two Prime Numbers, J. Rec. Math., 18 (1985), 22-24.
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LINKS
| T. D. Noe, Table of n, a(n) for n=1..25
Index entries for sequences related to decimal expansion of 1/n
C. K. Caldwell, The Prime Glossary, unique prime
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FORMULA
| a(n) = A061075(A007498(n)) [From Max Alekseyev (maxale(AT)gmail.com), Oct 16 2010]
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EXAMPLE
| 3 is the only prime p such that decimal expansion of 1/p has (nontrivial) period exactly 1.
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CROSSREFS
| Cf. A007498, A040017, A002371, A048595, A006883, A007732, A051626.
Sequence in context: A061075 A005422 A040017 * A065540 A084171 A192875
Adjacent sequences: A007612 A007613 A007614 * A007616 A007617 A007618
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KEYWORD
| nonn,nice,easy,base
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com), Robert G. Wilson v (rgwv(AT)rgwv.com), Mira Bernstein (mira(AT)math.berkeley.edu)
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